1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method for scheduling radio resources for semi-persistent uplink/downlink packet data transmission in a cellular wireless communication system, a structure of scheduling information, a scheme for transmitting the scheduling information, and an apparatus using the above-mentioned method and scheme as well as the scheduling information structure.
2. Discussion of the Related Art
A 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) communication system (hereinafter referred to as an “LTE system” for convenience of description) will hereinafter be described as an example of a mobile communication system applicable to the present invention.
A frame structure for use in the LTE system will hereinafter be described. The 3GPP LTE system supports a type 1 radio frame structure applicable to frequency division duplex (FDD), and a type 2 radio frame structure applicable to time division duplex (TDD).
FIG. 1 shows a structure of a type 1 radio frame used in the LTE system. The type 1 radio frame includes 10 subframes, each of which consists of two slots. A time length of each constituent unit is shown in FIG. 1.
FIG. 2 shows a structure of a type 2 radio frame used in the LTE system. The type 2 radio frame includes two half-frames, each of which is composed of five subframes, a downlink piloting time slot (DwPTS), a guard period (GP), and an uplink piloting time slot (UpPTS), in which one subframe consists of two slots. That is, one subframe is composed of two slots irrespective of the radio frame type. A time length of each constituent unit is shown in FIG. 2.
A resource grid structure for use in the LTE system will hereinafter be described in detail.
FIG. 3 shows an uplink (UL) time-frequency resource grid structure for use in the 3GPP LTE system.
Referring to FIG. 3, an uplink signal transmitted from each slot can be described by a resource grid including NRBUL NSCRB subcarriers and NsymbUL Single Carrier-Frequency Division Multiple Access (SC-FDMA) symbols. Here, NRBUL represents the number of resource blocks (RBs) in an uplink, NSCRB represents the number of subcarriers constituting one RB, and NsymbUL represents the number of SC-FDMA symbols in one uplink slot. NRBUL varies with an uplink transmission bandwidth constructed in a cell, and must satisfy NRBmin,UL≦NRBUL≦NRBmax,UL. Here, NRBmin,UL is the smallest uplink bandwidth supported by the wireless communication system, and NRBmax,UL is the largest uplink bandwidth supported by the wireless communication system. Although NRBmin, UL may be set to 6 (NRBmin,UL=6) and NRBmax,UL may be set to 110 (NRBmax,UL=110) the scopes of NRBmin, UL and NRBmax,UL are not limited thereto. The number of SC-FDMA symbols contained in one slot may be differently defined according to the length of a Cyclic Prefix (CP) and the spacing between subcarriers.
Each element contained in the resource grid is called a resource element (RE), and can be identified by an index pair (k,l) contained in a slot, where k is an index in a frequency domain and is set to any one of 0, . . . , NRBULNscRB−1, and l is an index in a time domain and is set to any one of 0, . . . , NsymbUL−1.
A Physical Resource Block (PRB) is defined by NsymbUL consecutive SC-FDMA symbols in a time domain and NSCRB consecutive subcarriers in a frequency domain. NsymbUL and NSCRB may be predetermined values, respectively. Therefore, one PRB in an uplink may be composed of NsymbUL×NSCRB resource elements. In addition, one PRB may correspond to one slot in a time domain and 180 kHz in a frequency domain. A PRB number nPRB and a resource element index (k,l) in a slot can satisfy a predetermined relationship denoted by
      n    PRB    =            ⌊              k                  N          sc          RB                    ⌋        .  
FIG. 4 shows a downlink (DL) time-frequency resource grid structure for use in the LTE system.
Referring to FIG. 4, a downlink signal transmitted from each slot can be described by a resource grid including NRBDL NSCRB subcarriers and NsymbDL OFDM symbols. Here, NRBDL represents the number of resource blocks (RBs) in a downlink, NSCRB represents the number of subcarriers constituting one RB, and NsymbDL represents the number of OFDM symbols in one downlink slot. NRBDL varies with an uplink transmission bandwidth constructed in a cell, and must satisfy NRBmin,DL≦NRBDL≦NRBmax,DL. Here, NRBmin,DL is the smallest uplink bandwidth supported by the wireless communication system, and NRBmax,DL is the largest uplink bandwidth supported by the wireless communication system. Although NRBmin, DL may be set to 6 (NRBmin,DL=6) and NRBmax,DL may be set to 110 (NRBmax,DL=110), the scopes of NRBmin, DL and NRBmax,DL are not limited thereto. The number of OFDM symbols contained in one slot may be differently defined according to the length of a Cyclic Prefix (CP) and the subcarrier spacing. When transmitting data or information via multiple antennas, one resource grid for each antenna port may be defined.
Each element contained in the resource grid is called a resource element (RE), and can be identified by an index pair (k,l) contained in a slot, where k is an index in a frequency domain and is set to any one of 0, . . . , NRBDLNscRB−1, and l is an index in a time domain and is set to any one of 0, . . . , NsymbDL−1.
Resource blocks (RBs) shown in FIGS. 3 and 4 are used to describe a mapping relationship between certain physical channels and resource elements (REs). The RBs can be classified into physical resource blocks (PRBs) and virtual resource blocks (VRBs). Although the above mapping relationship between the VRBs and the PRBs has been disclosed on a downlink basis, the same mapping relationship may also be applied to an uplink.
One PRB is defined by NsymbDL consecutive OFDM symbols in a time domain and NSCRB consecutive subcarriers in a frequency domain. NsymbDL and NSCRB may be predetermined values, respectively. Therefore, one PRB may be composed of NsymbDL×NSCRB resource elements. One PRB may correspond to one slot in a time domain and may also correspond to 180 kHz in a frequency domain, but it should be noted that the scope of the present invention is not limited thereto.
The PRBs are assigned numbers from 0 to NRBDL−1 in the frequency domain. A PRB number nPRB and a resource element index (k,l) in a slot can satisfy a predetermined relationship denoted by
      n    PRB    =            ⌊              k                  N          sc          RB                    ⌋        .  
The VRB may have the same size as that of the PRB. Two types of VRBs are defined, the first one being a localized VRB (LVRB) and the second one being a distributed type (DVRB). For each VRB type, a pair of VRBs in two slots of one subframe may assigned a single VRB number nVRB.
The VRB may have the same size as that of the PRB. Two types of VRBs are defined, the first one being a localized VRB (LVRB) and the second one being a distributed VRB (DVRB). For each VRB type, a pair of PRBs may have a single VRB index (which may hereinafter be referred to as a ‘VRB number’) and are allocated over two slots of one subframe. In other words, NRBDL VRBs belonging to a first one of two slots constituting one subframe are each assigned any one index of 0 to NRBDB−1 and NRBDL VRBs belonging to a second one of the two slots are likewise each assigned any one index of 0 to NRBDL−1.
In the LTE system based on an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, a resource area in which each UE is able to transmit or receive data to and from a base station (BS) is allocated from the BS to the UE. In this case, not only a time resource but also a frequency resource must be simultaneously allocated to the UE so as to complete resource allocation.
The so-called non-persistent scheduling method can simultaneously indicate time-frequency resource domains allocated to the UE. Therefore, if there is a need for the UE to use resources for a long period of time, it must repeatedly perform signaling for resource allocation, so that signaling overhead may be considerably generated.
In contrast, the so-called semi-persistent scheduling method first allocates a time resource to a UE. In this case, the semi-persistent scheduling method may allow the time resource allocated to a specific UE to have periodicity. Then, the semi-persistent scheduling method allocates a frequency resource to the UE when necessary to complete time-frequency resource allocation. The above-mentioned frequency resource allocation may be referred to as ‘activation’. When using the semi-persistent scheduling method, resource allocation can be maintained for a predetermined period by only one signaling process, so that resources need not be repeatedly allocated, resulting in reduction in signaling overhead. Thereafter, if the necessity of performing resource allocation for a UE disappears, a base station can transmit a signaling message for releasing the frequency resource allocation to the UE. In this way, the above-mentioned release of the frequency resource domain may be referred to as ‘deactivation’. In this case, it is preferable that the signaling overhead needed for the deactivation be reduced.